The present invention relates to a master magnetic information carrier such as a master disk used in preformatted recording of servo signals, address signals or regenerative clock signals of a magnetic recording medium, in particular, relates to a master magnetic information carrier having embedded magnetic layers that records the servo signals and the like, and a fabrication method thereof. The invention also relates to a magnetic contact duplication technology in a manufacturing process of a magnetic recording medium.
In a hard disk drive (hereinafter referred to as HDD), for example, recording and reproduction (or writing and reading) of data are processed while a magnetic head flies over a surface of a rotating magnetic recording disk by a floating mechanism called slider holding a flying height of several tens of nm. The bit information on the magnetic recording disk is stored in concentric data tracks on the disk. Read/write of the data is conducted by quickly moving and positioning the read/write head to the target data trace Each of concentric circles on the magnetic recording disk has preformatted fields recording in a certain angular interval the preformatted information including tracking servo signal for detecting relative position between the head and the data track, address signal or generative clock signal, and the data recording and reproducing head automatically detect its own position in a certain time interval. The preformatted information is written on the magnetic recording disk using a special writing apparatus called servo track writer after the disk is installed in a HDD, so that for the center of the writing signal of the preformatted information should not be off-centered from the disk center or the center of the head orbit.
In the meantime, recording density of the magnetic recording disk has currently reached as high as 20 Gbit/in2 in the development phase, and the recording capacity is increasing at a rate of 60% a year. Consequently, the density of the preformatted information for detecting the position of the head has necessarily increased. The prolonged time for writing the preformatted information is becoming a severe factor that lowers productivity of the HDD and raising its cost.
Recently, a preformatting recording technology has been proposed where whole of the preformatted information is transcribed at the same time in a areal manner by means of magnetic contact duplication technique utilizing a master disk, instead of linearly writing along each track utilizing a signal-writing head of the servo track writer. This technology is expected to shorten the preformatting time.
FIG. 10(a) through FIG. 10(c) and FIG. 11(a) and FIG. 11(b) illustrate the magnetic contact duplication technique. FIG. 11(a) is a cross sectional view showing an initial demagnetization process where permanent magnet 2 is moved in a circumferential direction above the surface of the magnetic recording disk 1. Since the structure of the magnetic recording disk 1 is well known, the figure simply shows a substrate 1a and a magnetic layer 1b laminated thereon. The magnetic layer 1b is not magnetized in one direction in the beginning, and is magnetized in the initial magnetization step uniformly in one direction, a circumferential direction, by leakage flux of the permanent magnet 2. The arrows in the magnetic layer 1b represent the direction of demagnetization field A. The curved arrow in FIG. 10(a) shows the moving path of the permanent magnet 2.
Then, a master disk for magnetic contact duplication is disposed in position on the magnetic recording disk 1 to which initial demagnetization has been performed, as shown in FIG. 10(b) and FIG. 1(b). Embedded magnetic films 3a, which are Co-based soft-magnetic films, are discretely embedded in surface region of the master disk 3, surrounded by surface portion 3b of the substrate.
Magnetic contact duplication is performed by moving the permanent magnet 4 on the master disk 3, as shown in FIG. 10(c) and FIG. 11(b). The curved arrow in FIG. 10(c) indicates the moving path of the permanent magnet 4. The magnetic field in the duplication step is the leakage flux from the permanent magnet 4, the direction of which is reversed from the demagnetization field A. During the movement of the permanent magnet 4, the leakage flux pass through the surface portion 3b of the substrate and reach the magnetic layer 1b of the magnetic recording disk 1 and reverse the field direction of the demagnetization A to produce recording magnetization B with high coercive force. In the embedded magnetic film 3a, in contrast, the leakage flux passes along the surface direction of the magnetic film so that magnetic resistance of the magnetic path is minimized. Since the leakage flux does not reach the magnetic layer 1b of the magnetic recording disk 1, the demagnetization A remains, thus a negative pattern of the pattern of the embedded magnetic film 3a is magnetically transferred onto the magnetic recording disk 1. In this magnetic contact duplication technique, the magnetic recording disk is not magnetized by leakage flux of the embedded magnetic film 3a of the master disk 3, but is selectively magnetized by the leakage flux from the permanent magnet 4 through the surface portion 3b of the substrate, while the embedded magnetic films 3a function as a magnetic contact duplication mask that shields parts of the leakage flux from the permanent magnet 4.
FIG. 12(a) through FIG. 12(e) show a method for manufacturing a master disk 3 having embedded magnetic films 3a. 
First, photoresist of 1 xcexcm thick is applied by spin-coating on a silicon substrate 3c of about 500 xcexcm thick, followed by patterning by means of photolithography commonly used in producing silicon semiconductor devices, to form an etching mask 5, as shown in FIG. 12(a). Then, grooves 6 of depth of about 500 nm are dug by dry-etching the surface of the silicon substrate 3c by means of reactive plasma etching technique using reactive gas of methane trichloride, as shown in FIG. 12(b). Then, Co-based soft-magnetic film 7 of about 500 nm thick is deposited by sputtering on the substrate with the mask 5 left thereon, to form an embedded Co-based soft-magnetic film 7 in the dug groove 6, as shown in FIG. 12(c). Finally, the resultant substrate 3c is dipped in solvent to remove the mask 5 and the Co-based magnetic film 7 thereon, remaining the Co-based soft-magnetic film 7 in the groove 6 as embedded magnetic films 3a. Thus, a master disk 3 with a flat surface having embedded magnetic films 3a is obtained.
The master disk manufactured by the above-described manner, however, involves the following problems.
FIG. 12(c) shows an ideal cross sectional structure in a deposition process of Co-based soft-magnetic film 7, where every sputtered Co particle travels to the bottom surface of the groove 6 of the substrate 3c with incident angle exactly perpendicular to the bottom surface and is not deposited on the inner side-wall of the groove 6 or side-wall of the mask 5. However, because the traveling particles include obliquely incident component as well as perpendicularly incident component, deposition occurs on the inner side-wall of the groove 6 and side-wall of the mask 5, as illustrated in FIG. 12(e), which is an enlarged cross section of the portion of FIG. 12(c) enclosed by two-dot chain line. Within the groove 6, depositing speed of the incident particles is fast due to shielding effect. Consequently, in the cross-sectional configuration after removing the mask 5 with solvent there are left recesses 8a and protrusions 8b, that are burrs of the pattern edges of the soft magnetic films, as shown in FIG. 12(f) which is an enlarged cross section of the portion enclosed by two-dot chain line in FIG. 12(d).
These recesses 8a and protrusions 8b cause various problems. Because the surface of the magnetic recording disk 1 contacts the surface of the master disk 3 or become close proximity with several tens to several hundreds of xc3x85 clearance between them in the magnetic contact duplication process, the protrusions 8b cause the magnetic recording disk 1 to be transferred with flaws and gouges in the magnetic contact duplication process. The recesses 8a on the surface of the master disk 3 also cause particles and chemical contaminants to be accumulated at the recesses. Those particles and chemical contaminants may be transferred to the magnetic recording disk 1 in certain probability after a large number of contact duplication operations.
Because the master disk 3 has to be closest to or directly contacted with the magnetic recording disk 1 to enhance accuracy of the magnetic contact duplication, the surfaces of the embedded magnetic films 3a and the silicon substrate 3c deteriorate by wear, for example.
In view of the foregoing, it is an object of the present invention to provide a master magnetic information carrier that has a flat surface free from protrusion and recess while having embedded magnetic film, and a method for manufacturing such a master magnetic information carrier.
It is another object of the invention to provide a master magnetic information carrier that reduces wear due to friction with a magnetic recording medium in a magnetic contact duplication process, a method for manufacturing such a master magnetic information carrier, and a method for manufacturing a magnetic recording medium
To accomplish the first mentioned object, the present invention features utilization of a resin substrate instead of a silicon substrate. That is, the master magnetic information carrier of the invention comprises embedded magnetic films surrounded by a surface portion of a resin substrate, the surface of the magnetic films being in a common plane with that of the surface portion of the resin substrate. By using the resin substrate, after forming discrete and isolated magnetic films on the substrate, step portions between the magnetic films can be made even with the surface portion of the resin substrate. The embedded magnetic films are surrounded by the surface portion of the resin substrate to obtain a smooth and flat surface and to avoid the protrusion and recess that would appear around each circumference of the embedded magnetic films. As a result, generation of flaws and gouges on the magnetic recording disk and transfer of particles and chemical contaminants to the recording disk in the contact duplication process can be avoided.
Material of the resin surface portion of the resin substrate may be the same as the material of the other portion of the resin substrate. In this case, the density in the resin surface portion is preferably higher than that in the other portion of the resin substrate, which enhances anchoring action with the embedded magnetic film and allows the use of a strong magnet for duplication. Further, the density distribution in the resin surface portion is favorable where the density varies in the surface direction such that the density becomes higher as a position approaches nearer to the side-walls of the embedded magnetic films. Also favorable is the density distribution of the resin surface portion where the density varies in the depth direction such that the density becomes higher as a position approaches nearer to the surface of the resin surface portion. The both density distributions enhance anchoring effect with the embedded magnetic films and durability of the magnetic films.
Material of the resin surface portion may be photo-setting resin. The resin surface portion made of the photo-setting resin may be formed after forming discrete and isolated magnetic films on a resin substrate, by applying fluid photo-setting resin and flattening it, followed by curing. Also in this construction, the embedded magnetic films are surrounded by the resin surface portion of the resin substrate to obtain smooth and flat surfaces and to avoid the protrusion and recess that would appear around each circumference of the embedded magnetic films. As a result, generation of flaws and gouges on the magnetic recording medium and transfer of particles and chemical contaminants to the recording medium in the contact duplication process can be avoided.
Preferably, a reinforcing substrate is laminated on the back surface of the resin substrate. By employing the configuration, warping and deformation of the resin substrate is minimized, and accuracy and durability of magnetic contact duplication can be enhanced.
A master magnetic information carrier of the invention may use a refractory substrate comprising a refractory base plate, such as silicon base plate. In that case, a master magnetic information carrier comprises an embedded magnetic films surrounded by resin surface portion of the refractory substrate, the surfaces of the magnetic films being in a common plane with the surface of the resin surface portion, wherein the material of the resin surface portion of the refractory substrate is thermo-setting resin. Since the refractory base plate is used in the substrate, material of the resin surface portion can be thermo-setting resin. Also in this configuration, the embedded magnetic films are surrounded by the resin surface portion to obtain a smooth and flat surfaces and to avoid protrusions and recesses that would appear around each circumference of the embedded magnetic films.
As a result, generation of flaws and gouges on the magnetic recording medium and transfer of particles and chemical contaminants to the recording medium in the contact duplication process can be avoided.
To accomplish the second object mentioned earlier, the master magnetic information carrier of the invention features provision of a protective film covering the embedded magnetic film. The protective film reduces friction in the magnetic contact duplication process and prolongs life of contact duplication operations.
The protective layer may be a double-layered film. Preferably, the lower layer is a DLC (diamond-like carbon) film and the upper layer is a lubricant film. The configuration remarkably prolongs life of contact duplication. When the protective film is a hydrogen-added DLC film, a film with higher hardness can be deposited than a pure DLC film. When the protective film is a nitrogen-added DLC film, adsorption of corrosive gases, dominant component of which is sulfide, is effectively suppressed.
The present invention further provides a method for manufacturing a master magnetic information carrier having embedded magnetic films surrounded by a resin surface portion of a resin substrate, the surface of the embedded magnetic films being in a common plane with the surface of the resin surface portion, the method comprising the steps of forming discrete and isolated magnetic films in a predetermined region by patterning a continuous magnetic film laminated on a surface of a resin base plate, and pressing the heated resin substrate from above the isolated magnetic films by a die.
According to the manufacturing method, the resin surface portion is formed by a marking or stamping method, in which the surface region within the resin base plate itself is thermoplastically deformed. Therefore, the resin surface portion and the other portion of the resin substrate are in an integrated structure without any boundary in-between. The resin surface portion is denser than the other portion of the substrate because of the pressure molding adapted in the manufacturing method. The resin surface portion exhibits density distribution both in the surface direction or lateral direction and in the depth direction or vertical direction in the resin surface portion, which brings about the strong anchoring effect with the embedded magnetic films, eliminating risk of peeling off of the embedded magnetic films even when the magnetic force of the permanent magnet for magnetic contact duplication is strong.
The manufacturing method of the invention may further comprise a step of coating the surface of the resin substrate with photo-setting resin film between the step of forming isolated magnetic film and the step of pressing the substrate with die, and also comprise a step of irradiating light from the back surface side of the resin substrate before releasing the die utilized in the pressing step. The resin surface portion with reduced strain and initial stress is obtained by the method.
Preferably, the recess portion of the die is adjusted to the position opposite the predetermined region for the magnetic film in the resin substrate and pushed down. In such a process, the protrusion portion of the die first sink into the resin substrate, and then, the recess portion of the die catches the predetermined region within the recess portion of the die and presses the isolated magnetic films into the resin substrate. Consequently, the embedded magnetic films hardly drift relative to each other, and precise positioning of the embedded magnetic film is achieved. In addition, the region formed by the protrusion portion of the die is useful as an air vent groove.
The present invention provides further method for manufacturing a master magnetic information carrier having an embedded magnetic films surrounded by a resin surface portion on a refractory base plate, the surfaces of the embedded magnetic films being in a common plane with the surface of the resin surface portion, the method comprising the steps of forming discrete and isolated magnetic films in a predetermined region by patterning a continuous magnetic film deposited on a surface of the refractory base plate, applying fluid thermosetting resin covering the isolated magnetic films on a refractory base plate, curing the fluid thermosetting setting resin by heating, and etching-back a film of the cured thermo-setting resin until a surfaces of the isolated magnetic films is exposed.
The method proceeds with the sequence of forming the isolated magnetic films, covering the magnetic films with the thermo-setting resin film and curing, and etching-back the resin film. Therefore, the surfaces of the embedded magnetic films and the resin surface portion of the substrate can be made smooth and flat, to obtain a master magnetic information carrier free from protrusion and recess at the boundaries between the magnetic films and the resin surface portion.
The invention further provides a method for manufacturing a magnetic recording medium including a preformatting step performing magnetic contact duplication from a master magnetic information carrier to a magnetic recording medium, wherein contact duplication is conducted with the master magnetic information carrier overlapped together with the magnetic recording medium, and the two articles immersed in liquid of a lubricant or exposed to vapor of a lubricant. Since friction is reduced with the liquid or vapor of the lubricant, prolonged life of contact duplication times is achieved even in a master magnetic information carrier without protective film.